A NATO summit set for Warsaw in July comes at a “critical time” as the alliance deals with Russian assertiveness and the threat of terrorism amid other challenges, Secretary-General Jens Stoltenberg said Tuesday.

Stoltenberg was speaking following talks with Poland's Defense Minister Antoni Macierewicz, who said that a bigger NATO presence in Eastern Europe would mean a greater sense of security for Poland.

They were discussing preparations for the July 8-9 summit, which is to decide how many additional NATO troops will be deployed on the eastern flank, and where exactly. Concerned over Russia's actions, Poland has been seeking a significant, permanent NATO presence on its territory and the region.

Stoltenberg said the summit comes amid a “more assertive Russia, intimidating its neighbors, and changing borders by force,” violence in North Africa and the Middle East and terrorism, cyberattacks and ballistic missile proliferation.

He said NATO is responding by “implementing the biggest reinforcement of our collective defense since the end of the Cold War.”

In Moscow, Deputy Foreign Minister Alexei Meshkov said Russia will take measures in response to an increased NATO military presence close to its borders, but did not give details.

“We have to ensure the security of our state,” Russia's TASS agency reported Meshkov as saying.

NATO's enhanced presence already includes a significant increase in the number of troops ready for quick reaction, speeding up decision-making and holding a greater number of major international military exercises, like Anaconda-16, which will involve some 30,000 troops in Poland in June.